The present invention relates to a multifocal lens capable of providing a wearer with a focused vision in a range of distances and of a method of utilizing same for treating an individual suffering from a visual disorder such as presbyopia. More particularly, the present invention relates to a simultaneous multifocal contact lens which employs overcorrection of a near vision additional correction of a peripheral near vision focal region to thereby provide a wearer with a complete range of focused vision, in particular focused near vision.
As an individual advances in years, typically past 40-45, a physiologic loss of accommodation in the eyes begins. This physiological loss, which is termed presbyopia, is characterized by an inability to focus on objects that are relatively near to the individual (typically less then 22 cm). In addition to aging, a variety of eye disorders, such as, for example, cataract, which often necessitates lens replacement, can also abolish an individual""s ability to focus throughout a range of distances.
To correct the loss of a vision range, individuals rely upon spectacles, contact lenses or ophthalmic lens (in the case of lens replacement) having a number of different regions with different optical powers in order to find the appropriate optical power for the object or objects upon which the observer wishes to focus.
With spectacles, the process involves shifting the field of vision from typically an upper lens portion far power to a lower lens portion near power. With contact lenses, however, this approach has been less than satisfactory.
The prior art teaches two types of contact lens designs for the correction of presbyopia, alternating (or translating) and simultaneous.
The design of alternating (or translating) lenses is very similar to bifocal eyeglass lenses in that the wearer sees through the distance segment in the upper portion of the lens when looking straight ahead and sees through a lower near vision segment when the eye is moved to look down. The translation from distance to near in these lenses is achieved through the mechanical action of the lens resting on the lower eyelid and, when the eye looks down, the lens remains stable on the lower eyelid causing the pupil of the eye to translate from the distant vision portion of the lens to the near vision portion of the lens. As such, when fabricated from soft materials, numerous operational problems plagued these lenses which have, therefore, enjoyed very limited commercial success.
The design of simultaneous vision bifocal or multifocal contact lenses is either concentric or aspheric with focal power changing through different areas of the lens. These lenses are fitted so that distance, intermediate and near zones focus images simultaneously on the retina of the eye and the brain then separates out the image desired.
Theoretically, with adaptation, the ability to change focus naturally from near to far with no blurring in between can be achieved with simultaneous vision lenses.
As alternating presbyopic designs proved to be unsuccessful in soft contact lens designs, most of the development work with soft contact lenses was done in the area of simultaneous presbyopic correction with concentric designs or aspheric designs. Numerous examples of simultaneous bifocal contact lenses or ophthalmic lens exist in the art.
For example, U.S. Pat. No. 4,923,296 to Erickson describes a lens system which comprises a pair of contact lenses, each having equal areas of near and distant optical power, with the lens for one eye having a near upper half and a distant lower half and the lens for the other eye having a distant upper half and near lower half. Together they provide at least partial clear images in both eyes, and through suppression by the brain of the blurred images, allow alignment of the clear images to produce an in-focus image.
U.S. Pat. No. 4,890,913 to de Carle describes a bifocal contact lens comprising a number of annular zones having different optical powers. The object in the design of this lens is to maintain, at all times, regardless of pupil diameter, an approximately equal division between near and distant powers, which requires between six and twelve total zones on the lens.
Another attempt at providing a bifocal contact lens is described in U.S. Pat. No. 4,704,016 to de Carle. Again, this lens attempts to maintain, at all times, regardless of pupil diameter, an approximately equal division between near and distant powers.
Yet another attempt at providing a bifocal contact lens is described in U.S. Pat. No. 5,929,969. This lens comprises a number of circular ring zones of two optical powers.
Although the above described bifocal lenses provide some vision correction, a mismatching of the various optical zones may lead to destructive interference and thus a less than optimal vision in some instances.
In addition to bi-focal lenses, a number of multifocal lenses which attempt to improve upon their bifocal counterparts have also been described.
For example, U.S. Pat. No. 5,448,312 describes a multifocal concentric ophthalmic lens for presbyopic patients constructed with three general annular lens portions in a multifocal design. A central circular portion of the lens has only the patient""s distance corrective power, and is surrounded by a first inner annular portion, which can consist of multiple annular rings having an inner radial portion which enhances the patient""s near focal power encircled by radial portions of substantially equal cumulative amounts of distance and near optical power focal correction for the patient. This is surrounded by a second outer annular portion, which can also consist of one or more annular rings having additional distance focal power near the periphery of the optical surface area of the ophthalmic lens. Each annular ring has either a near or distance optical power and works in combination with other lens portions to yield the desired focal ratio in that portion of the lens.
U.S. Pat. No. 5,682,223 describes a multifocal lens design with near, far and intermediate optical power zones. The borders of these zones are optimized for pupil size as a function of lighting conditions.
In this design, zone placement and zone radii are not carefully planed and as such destructive interference cannot be avoided.
To overcome interference problems, U.S. Pat. No. 5,982,543 describes a multi refractive zone lens optimized with consideration for phase match between the zones.
However, the lens design described features lens coherence properties in visible light which vary considerably from one scene to the next.
Although some of the above described lenses have traversed some of the limitations inherent to multifocal lenses, these lenses still provide sub-optimal vision correction for some or all vision ranges.
The above described prior art designs, be it aspheric or concentric, cannot provide monocular multifocal correction for moderate to mature presbyopia. In most cases, some form of modified monovision is required in an attempt to satisfy the visual requirement for near and far vision.
To address this and other problems typical of prior art simultaneous multifocal lenses a variety of lenses with under or over corrected focal regions have been described.
For example, U.S. Pat. Nos. 5,864,378 and 5,864,379 describe a contact lens and an opthalmic lens (respectively) in which a central near vision zone (""379), or both a central near vision zone and a peripheral far vision zone (""378) are overcorrected. According to these patents, while such a correction does not impair distance vision, it compensates for presbyopia and therefore allows a user to focus on objects within a range of near and intermediate distances.
U.S. Pat. Nos. 5,919,229 and 5,702,440 both describe contact lenses with undercorrected peripheral near vision zones.
Although these lenses substantially enhance the focus range of an individual as compared to other prior art designs, such lenses still suffer from limitations which arise from the nature of the correction or the lens position of the vision region which is corrected. As such, these prior art lens designs cannot completely compensate for moderate to severe presbyopia, thus resulting in a less than a complete range of focused vision.
There is thus a widely recognized need for, and it would be highly advantageous to have, a simultaneous multifocal lens which can overcome presbyopia, thus providing a complete range of focused vision, in particular focused near vision, while at the same time having a relatively short period of visual adjustment and being comfortable to the wearer.
According to one aspect of the present invention there is provided a simultaneous multifocal contact lens for correcting vision acuity of an individual, the contact lens comprising a central region radially surrounded by at least one far vision focal region and at least one near vision focal region, wherein a near vision additional correction of the at least one near vision focal region is overcorrected by at least 10% with respect to the near vision additional correction prescribed for the individual according to a standard prescription for lens radius design.
According to another aspect of the present invention there is provided a method of improving visual acuity in an individual suffering from presbyopia, the method comprising the steps of (a) fabricating, according to a prescription of the individual, a pair of simultaneous multifocal contact lenses each including a central region radially surrounded by at least one far vision focal region and at least one near vision focal region, wherein a near vision additional correction of the at least one near vision focal region is overcorrected by at least 10% with respect to the near vision additional correction prescribed for the individual according to a standard prescription for lens radius design; and (b) fitting the individual with the pair of simultaneous multifocal contact lenses to thereby improve the visual acuity of the individual.
According to further features in preferred embodiments of the invention described below, the near vision additional correction of the at least one near vision focal region is overcorrected by 10 to 100% with respect to the near vision additional correction prescribed for the individual according to the standard prescription for lens radius design.
According to still further features in the described preferred embodiments the near vision additional correction of the at least one near vision focal region is overcorrected by 15 to 70% with respect to the near vision additional correction prescribed for the individual according to the standard prescription for lens radius design.
According to still further features in the described preferred embodiments the near vision additional correction of the at least one near vision focal region is overcorrected by 20 to 50% with respect to the near vision additional correction prescribed for the individual according to the standard prescription for lens radius design.
According to still further features in the described preferred embodiments a surface of the simultaneous multifocal contact lens which lies adjacent to a cornea of the individual is quadrically aspherically shaped with substantially identical eccentricity throughout and a substantially constant radius for each of the at least one near and the at least one far vision focal regions.
According to still further features in the described preferred embodiments the at least one near and the at least one far vision focal regions are each shaped as distinct rings.
According to still further features in the described preferred embodiments the focal regions radiate outwardly from the central region in an alternating sequence including the far vision focal region and the near vision focal region.
According to still further features in the described preferred embodiments the sequence is repeated at least twice.
According to still further features in the described preferred embodiments the sequence is repeated at least three times.
According to still further features in the described preferred embodiments the focal regions radiating outwardly from the central region are positioned 1.125, 1.275, 1.525, 1.675, 1.9 and 4.0 mm from a center of the central region.
According to still further features in the described preferred embodiments the simultaneous multifocal lens further comprising a tri-focal diffractive microrelief profile region being positioned at an outermost region of the simultaneous multifocal lens and being for ensuring in-phase interference of the at least one near vision focal region and the at least one far vision focal region when each being at a proper focus.
According to still further features in the described preferred embodiments the simultaneous multifocal contact lens further comprising at least one intermediate vision focal region radially surrounding the central region.
According to still further features in the described preferred embodiments a surface of the simultaneous multifocal contact lens which lies adjacent to a cornea of the individual is quadrically aspherically shaped with substantially identical eccentricity throughout and a substantially constant radius for each of the at least one near, the at least one intermediate and the at least one far vision focal regions.
According to still further features in the described preferred embodiments the at least one near, the at least one intermediate and the at least one far vision focal regions are each shaped as distinct rings.
According to still further features in the described preferred embodiments the focal regions radiate outwardly from the central region in an alternating sequence including the far vision focal region, the intermediate vision focal region and the near vision focal region.
According to still further features in the described preferred embodiments the sequence is repeated at least twice.
According to still further features in the described preferred embodiments the sequence is repeated at least three times.
According to still further features in the described preferred embodiments the near and intermediate focal regions radiate outwardly from the central region in an alternating sequence.
According to still further features in the described preferred embodiments the sequence is repeated at least twice.
According to still further features in the described preferred embodiments the sequences are surrounded by the at least one far vision focal region.
According to still further features in the described preferred embodiments the focal regions radiating outwardly from the central region are positioned 1.275, 1.525, 1.675, 1.9 and 4.0 mm from a center of the central region.
According to still further features in the described preferred embodiments the simultaneous multifocal lens further comprising a tri-focal diffractive microrelief profile region being positioned at an outermost region of the simultaneous multifocal lens and being for ensuring in-phase interference of the at least one near vision focal region, the at least one intermediate vision focal region and the at least one far vision focal region when each being at a proper focus.
According to still further features in the described preferred embodiments the central region is a far vision focal region.
According to still further features in the described preferred embodiments the central region is a near vision focal region.
According to still further features in the described preferred embodiments the near vision additional correction of the central region is as prescribed for the individual according to the standard prescription for lens radius design.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a multifocal lens capable of providing a wearer with a focused vision in a range of distances which is superior over prior art designs because apparently it accounts for distortions of base curve radii for near vision optical regions associated with contacting the lens with an eye.